Chrome 46 postpones the media playback in the background tabs until the tab is foregrounded

What this means

If you’ve opened a tab specifically in the background, an ad or video/audio won’t play automatically until that tab is forgrounded or gains focus. “Resources will still be preloaded if indicated but Chrome will delay the start of playback until you actually visit the tab.”

“Videos which autoplay in the background will now have their loaddeferred until the tab is visible for the first time — this avoidsautoplay during session restore and premature playback.”